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  1. #1
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    How does refrigerant become able to absorb heat

    I got a question someone asked me the other day and I wasn't 100% sure on it. We're talking commercial walk in units.

    When refrigerant goes through the metering device, it goes in as high pressure liquid and once on the other side of it, it's low pressure liquid but now it's cool liquid (27*F or so).

    What I understood is compressed liquid once sprayed out as vapor it gets cold in the phase change, but really, there is no phase change as it's still liquid, then it runs through the evap and THEN becomes gas.

    I think i got some stuff messed up and I wanted to get it cleared up.

    Thanks in advance.

  2. #2
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    When it goes through the metering device, the pressure drops... some of the refrigerant evaporates, to cool off the rest of the refrigerant...this is called flash gas. Then, the now cold refrigerant starts boiling when the warm air hits the coil. Eventually the refrigerant all boils, and then starts getting superheated by the warm air over coil.

  3. #3
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    The whole deal is the pressure temperature relationship with the refrigerant. That's where the magic is.

    Take 40 water in a garden hose and put your thumb over the end of the hose and you will get a spray of water that's about the same temperature no matter which side of your thumb the temperature is measured.

    Now try the same thing with refrigerant. If the pressure is higher on one side of your thumb than it is on the other side, that refrigerant will be at very different temperatures.

    You can actually plot it out on a chart. That's what makes it so special.

    Water might not have been the best example because it can act like a refrigerant under certain conditions too (like when it gets to 212F), but you get the idea.

  4. #4
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    Its a boiling liquid when it comes out of the metering device. So its absorbing heat immediately when it exits the metering device.
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  5. #5
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    You guys mentioned phase change. Where does that take place and why do you want it there? I'm just pushing the subject a little because phase change is important.
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  6. #6
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    Quote Originally Posted by WAYNE3298 View Post
    You guys mentioned phase change. Where does that take place and why do you want it there? I'm just pushing the subject a little because phase change is important.
    All good answers so far, but "Phase Change" is a poor choice of words imo. Try to use "Change of State", ie. from a vapor to a liquid, and back again. "Refrigerant Cycle":From the comp. discharge, hot high pressure vapor, thru the condenser and out, then hot high pressure liquid, thru the metering device and out, then cold low pressure vapor, to the suction inlet of the comp. and the cycle begins again. Now i know there are 2 places where the refrigerant will be a combination of both liquid and vapor, in the condenser and in the evap., so don't be too hard on me for not adding them. OP:Tell your friend that everything contains heat, and cold is the absence of such heat. PS, good ref. reading below.

    https://www.achrnews.com/articles/11...tioning-part-1

  7. #7
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    Phase change or change of state in my opinion are more descriptive than heat of vaporization but none of them are poor choices because they mean the same thing. It's kind of like car or four passenger automobile.
    No man can be both ignorant and free.
    Thomas Jefferson

  8. #8
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    The short...and perhaps the most clear way of looking at this is...the refrigerant is changing state from a liquid to a vapor, and in order to change its state, it needs to take on heat. It is that "taking on heat" which causes the refrigeration effect. As the heat is being taken out of that walk in box, it is latently transported to the condensing unit, where it is ejected to atmosphere during the process of condensation back into a liquid, using that condensing unit up on the roof.
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  9. #9
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    Quote Originally Posted by WAYNE3298 View Post
    Phase change or change of state in my opinion are more descriptive than heat of vaporization but none of them are poor choices because they mean the same thing. It's kind of like car or four passenger automobile.
    Do you also agree that freon is a proper word to describe all refrigerants? Use the proper terminoiogy and real professional hvac/r techs will respect you for it.

  10. #10
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    It depends on who you are talking to Izenglish. Take for example what most people call a freeze plug on a car engine. It isn't a freeze plug even though it could pop out if the water in the block freezes. Or how about calling a car engine a motor. Compressed air has been used as a refrigerant and is still used in some cases. What is your point anyway??
    No man can be both ignorant and free.
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  11. #11
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    Freon is a registered Dupont trademark for an entire family of refrigerants, which is why it is so often used to describe any vapor compression refrigerant in use in any system.

    It is imprecise, but it is not technically incorrect....as long as it is a Dupont product.
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  12. #12
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    Latent heat of evaporation. TB said it well.

    In a correctly operating system, the theory is that only in the last pass in the evap coil is "dry." This is how we charge to super heat. The refrigerant does not change temperature until it is no longer saturated and then starts increasing in temperature.

    Same basic concept in reverse for the condenser coil.... Subcooling.

  13. #13
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    Thread Starter
    I got what you are all saying, I'm talking right as it exits the TXV.

    You have liquid refrigerant coming out of the condenser which is above 27*F, so how does it get down to such a low temp? I get that it absorbs the heat as a liquid and boils off, but it's absorbing heat from the air in the fridge.

    But in order for it to absorb heat from 38*F air, the refrigerant has to be cooler. So how does it get from room temp (72*F) or slightly above down to 27*F from the inlet of the xpansion valve to the outlet, that's what I don't understand.

    Is it really the flash gas that cools down the liquid to that point?

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